The present disclosure relates to a rotary-wing aircraft, and more particularly, to a rotary-wing aircraft having an electric propulsion system with an overrunning clutch.
Conventional rotary-wing aircraft typically utilize a mechanical drive train to transmit power from one or more engines to drive main and tail rotor systems. The helicopter mechanical drive train may include a main rotor gearbox, an intermediate gearbox, a tail rotor gearbox and their inter-connecting shafts. The main rotor gearbox converts the high speed input from each engine to a low speed output for the main rotor system. The main rotor gearbox may also provide power take-offs to drive an anti-torque system, a hydraulic system and other such systems.
The mechanical drive train may further include an overrunning clutch. The overrunning clutch in a traditional helicopter allows the rotor speed to exceed the motor or drive speed. The overrunning clutch thus prevents rotor over speed from back driving the engine, and, in an engine out situation, the overrunning clutch eliminates the engine drag (torque opposing rotation) from retarding the ability of the rotor to freely spin, or autorotate. The overrunning clutch is typically mounted to the input stage of the gearbox where the rotation speed is high and the torque is low, and typically yields the lowest weight clutch mechanism possible. Traditionally, a sprag clutch is utilized as its high speed and limited torque capability make it ideal for that application. However, while in the overrunning mode, the cam elements (torque transfer members) in this clutch design continue to stay in contact with both the clutches inner and outer hub, requiring continuous oil lubrication to minimize heat and wear on the components.
While such arrangements have generally satisfied the requirements for traditional rotor systems, the art would be receptive to improved methods and systems for clutch arrangements in rotary-wing aircraft.